Investigation on the microstructure and composition segregation of the laser metal forming directional solidification

Laser metal forming directional solidification experiments were performed by using nickel-base superalloy as substrate and powder Rene95 as cladding material. The solidification microstructure of the cladding layer was investigated. According to the theory of columnar/equiaxed transition (CET) in front of the solid/liquid interface, it was found that, in the single path multi-layer cladding layers and multi-path multi-layer cladding layers, the microstructure with the same crystallographic orientation as the substrate was obtained by reasonably selecting the processing parameters. Round directional solidification sample of laser multi-layer cladding was acquired by combining the multi-layer laser cladding and computerized numerical control (CNC) technique. The microstructure of the cladding layers is consisted of regular columnar dendrites. The primary spacing of dendrites is about 5-30 m and the secondary arm is small or even degenerated. Energy spectrum analysis showed that there was no obvious composition segregation in the cladding layers.